1. Field of the Invention
The present invention relates to quick change chucks for power tools and, more particularly, to a new chuck that provides a significantly increased holding force without sacrificing ease of tool changing.
2. Discussion of Related Art
Although there are a number of existing chucks and like devices for retaining cutting bits in power tools and driven spindles, they all have some disadvantages which detract from their advantages. For example, while some chucks hold the cutting tool with enough force that slippage will not occur, the changing of the tool can be very cumbersome and time consuming. Others allow an easy changing of tools but do not provide enough holding torque to prevent slippage from occurring. There are a few chucks that allow easy changing of tools and also provide a reasonable amount of holding torque. However, at the present time, there are no chucks currently available which allow an easy change of the cutting tool and which also provide the increase in mechanical advantage in an amount sufficient to effect a compressive force along a circumferential surface of a tool shank or collet to substantially increase the holding torque. A chuck of this type would allow the power tool user to spin much larger cutting tools at higher speeds while still maintaining a substantially greater safety margin because of the increased holding force.
One chuck of particular interest here is that disclosed in U.S. Pat. No. 5,096,212 to Walsh. Although this chuck has advantages, there are several disadvantages to the chuck. By way of background, it is noted that routers are required to spin the cutting bit at a relatively high angular speed, typically above 20,000 rpm. Thus, the design of a router chuck has to be as lightweight and compact as possible for obvious reasons. Accordingly, if the chuck is relatively heavy and bulky in size as in the case of the chuck of the Walsh patent, unwanted and sometimes severe vibration can occur, resulting in an unsafe operating condition. Further, the chuck of the Walsh patent requires two cams which secure the tool essentially by pinching the tool shaft. Since the cams are harder than the typical tool shaft, an unwanted indentation in the tool shaft can result if the cams are over-tightened. Another disadvantage of the Walsh chuck is that the manner in which the nut is attached to the body is inadequate. In this regard, although during the short time a chuck constructed as disclosed in the Walsh patent was distributed no failures were reported, the construction could have eventually led to catastrophic failure. Finally, the construction of the chuck of the Walsh patent employs some unnecessary parts, includes a relatively weak screw, and in general, has the appearance of being cumbersome and awkward to use.
An improvement in the Walsh construction of quick change router chucks and the like is disclosed in U.S. Pat. No. 6,332,619 to DeRosa. The genesis of this construction was an attempt to overcome all, or as many as possible, of the shortcomings of the Walsh chuck. The attempt was successful and the construction of the DeRosa chuck not only incorporates several improvements but has been manufactured and sold in quantity to the general public. One improvement is the use of only a single cam instead of two. The single cam was also modified and is allowed to slightly crush under pressure. However, while the cam maintains its holding power, it does not indent the tool shaft. The nut is attached by the use of retaining rings which are much stronger and safer than the previously used pins. Among other advantages, the size of the chuck was greatly reduced by the elimination of one cam and a few unnecessary internal parts, and a stronger screw was incorporated. However, one disadvantage is that some of the holding power provided by the chuck had to be sacrificed by the use of the softer cam in eliminating the tool shaft indentation problem created by the previous use of a harder cam.
U.S. Pat. No. 4,211,510 ('510) is directed to an adjustable boring tool that includes a shaft having a longitudinal axis, and a cylindrical bore for mounting a cylindrical boring bar that may adjusted to effect the boring diameter of the cutting tool. To effect the boring diameter adjustment, the longitudinal axes of the bore and boring bar are offset a predetermined amount from the longitudinal axis of the shaft, which is offset and allows adjustable radial position of the tool cutting point. A transverse slot extends to the center line of the cylindrical bore and intersects a diagonal slot that extends in the plane of the longitudinal sectional view and terminates along a diagonal line to define two split quadrant bore half segments that both are deflected to force the bar into clamped engagement between the wall segments. A transverse clamp screw on one side of the bore tightens the quadrant wall segments while the boring bar is in an adjustable position within the cylindrical bore and clamps the slotted segments against the boring bar. A graduated dial fixed to the boring bar permits an accurate, calibrated adjustment of the effective diameter of the cutting point through rotation of the boring bar, when not clamped in place, over a range equal to four times the offset. The spindle mounting shafts shown in the drawings of the '510 patent are commonly used and may be mounted in a standard milling machine. At rotational routing tool speeds of up to more than at least about 20,000 rpm, and in a range of from about 8,000 to 25,000 rpm as used in the current invention, the required offset axes of the '510 patent would cause vibration of the tool that would make it unusable and unsafe as a routing tool holder.
U.S. Pat. No. 6,908,264 ('264) is directed to a specially modified quick-change core drill that is not attached to the drill motor in the standard way by the use of threads. It is not a chuck, but is a modified hole or circular saw that does not contain the usual mounting threads at one end. Instead, the modified core drill contains an L-shaped channel formed by a pair of slots that allow the modified core drill to be locked into an adapter with a locating stop. Since both ends of the modified core drill are open, the removal of the core after drilling becomes very easy. In a core drill application, the threads on the drill motor absorb all of the tangential loading and the front bearing in the drill motor absorbs all of the axial load thereby acting as a thrust bearing. This is the way standard core drills are commonly attached to slow speed, high torque core drill motors. The adapter comprises a first end adapted to be removably connected to the drill motor, and a second end adapted to be removably connected to a modified core drill.
Core drilling of the '264 patent, whether using a diamond or carbide core drill, is accomplished at very slow rotational speeds (50-1000 rpm) in order not to destroy the cutting edges of the core drill. However, an increased length to any given diameter is characteristic of a typical core drill. If the standard rotational speed of the core drill motor is increased to a much higher value, the cutting edges on the core drill would become damaged, and vibration would begin and become increasingly apparent as the rotational speed is further increased. Thus making the mechanical configuration of the drill and adapter unstable and usable at typical routing tool speeds.
Although the '264 patent slots 32 and 34 along with screw 30 do aid in holding the modified core drill, pin 24 absorbs the major portion of the tangential loading along with the L-shaped slot 19 and 42. This configuration acts as a positive stop in a similar manner as the threads on a standard core drill. This would prevent the modified core drill from slipping in the adapter thereby damaging both the core barrel and adapter in the event of a jam, which is common in core drilling. Upon detection of a jammed core inside the core drill barrel, the '264 patent device user can quickly and easily remove the jammed core from the drill barrel by disconnecting the modified core drill from the adapter. Since there are no obstructions present, the user can simply remove the jammed core from the first end of the core drill barrel.
The '264 device also requires a modified core drill to function with the adapter, which will not receive a stock core drill. Since core drills come in many lengths and diameters, a modified core drill barrel has to be manufactured for each diameter and length. Depending on the required depth of cut, the core drill and adapter have to be of a different diameter and/or length for the adapter to maintain axial stability of the core drill. Moreover, core drills usually require long lengths with respect to their diameter because of their intended application. Such a configuration has an increase bending moment and is, therefore, prone to vibration or instability at elevated rotational speeds.
In a routing application, the ratio of the axial length of the chuck divided by its outside body diameter should be held to the lowest value as practical (short and fat) to minimize vibration at high speeds. The ratio of the minimum axial length of my chuck divided by the diameter of its bore should be no less than at least 2 to 1 to maintain adequate stability and gripping force at high speeds. However, in a core drill application, the adapter of the modified '264 patent core drill requires a ratio of its axial length divided by its outside diameter to be large (tall and thin), thus giving it stability for operating the core drill at higher axial loads at lower speeds. This is opposite to what is required in a router application making the two applications completely different from each other so that their respective operating principles are not interchangeable.
Excessive spindle speed for axially loaded tools will cause premature tool wear, breakages, and can cause tool chatter, all of which can lead to potentially dangerous operating conditions. In contrast to the prior art related to adjustable boring tools discussed hereinabove, alignment of router chucks, routing tools, and coupling parts used to attach chucks to router spindles is critical to avoid failure due to vibration at the high rotational speeds required for routing materials.
Axial feed rates for prior art core drilling devices are very low (0.1 to 4 inches per minute), the axial loads are very high and the drill has to be able to produce a very high torque. Such prior art devices may be manufactured with loose tolerances in their threaded connections and axial offsets of their tool with respect to their coupling mechanisms because of their slower rotational speeds compared those used in routing operations.
Very high router feed rates produce loads that are laterally induced normal to the longitudinal axis of a router tool, and are thus opposite to the axial loads induced parallel to the longitudinal axis of a core drill tool. High router rotational speeds reduce the load per tooth on the router cutting tool and reduces chatter that is caused by the tool bouncing on and off the workpiece due to high rotational speed and/or feed rate. For these reasons, nothing in the prior art mechanical structures dealing with axial loads suggests to a person ordinarily skilled in the routing art how to deal with solving problems related to primarily laterally induced loads on cutting tools.